1. Field of the Disclosure
The disclosure relates in general to broadband networks and, more particularly, to a bridge for use with optical fibers in a broadband network.
2. Background Art
Fiber optic communications are a method of transmitting information by sending pulses of light through an optical fiber. The light forms an electromagnetic carrier wave that is modulated to carry information. Fiber optics communications are useful in broadband networks for telecommunications, data transmission, internet communications, high definition (HD) television, digital video streaming, video on demand (VOD) and other communications.
Due to much lower attenuation and interference, optical fibers provide many advantages over existing copper wire in long-distance and high-demand applications. Because of its advantages over electrical transmission, optical fibers have largely replaced copper wire in networks.
Fiber optic communications can include: transmitting the optical signal, relaying the signal along the fiber, maintaining the strength of the signal so that it does not become too distorted or weak, receiving the optical signal, and converting it into an electrical signal. Fiber optic communication systems usually have: an optical transmitter to convert an electrical signal into an optical signal to send into the optical fiber, a cable containing bundles of multiple optical fibers that are routed through underground conduits and buildings, multiple kinds of amplifiers, and an optical receiver to recover the signal as an electrical signal. The information transmitted is often digital information generated by computers, telephone systems, and cable television companies.
Hybrid fiber-coaxial (HFC) is a telecommunications industry term for a broadband network which combines optical fibers and coaxial cable. It has been commonly employed globally by cable television operators. The fiber optic network can extend from the cable operators' headquarters or master headend, sometimes to regional headends, then to a neighborhood's hub site, and subsequently to a fiber optic node which can serve numerous locations, such as 25 to 2,000 homes. A regional or area headend or hub can receive the video signal from the master headend and add to it the public, educational, and government access cable TV channels as required by local franchising authorities, or insert targeted advertising that would appeal to a local area. The various services are encoded, modulated and converted onto radio frequency (RF) carriers, combined onto a single electrical signal and inserted into a broadband optical transmitter. The optical transmitter converts the electrical signal to a downstream optically modulated signal that is sent to the nodes. Fiber optic cables can connect the headend or hub to optical nodes. A fiber optic node can have a broadband optical receiver which converts the downstream optically modulated signal coming from the headend or hub to an electrical signal going to the homes.
The optical portion of the network can provide a large amount of flexibility. If there are not many fiber optic cables to the node, wavelength division multiplexing can be utilized to combine multiple optical signals onto the same fiber. Optical filters are used to combine and split optical wavelengths onto the single fiber.
The coaxial portion of the network can connect numerous locations, such as 25 to 2,000 homes, in a tree-and-branch configuration off of the node. Radio frequency (RF) amplifiers can be used at intervals to overcome cable attenuation and passive losses of the electrical signals caused by splitting or tapping of the coaxial cable. Trunk coaxial cables can be connected to the optical node and form a coaxial backbone to which smaller distribution cables connect. Trunk cables also carry alternation current (AC) power which can be added to the cable line by a power supply. From the trunk cables, smaller distribution cables can be connected to a port of the trunk amplifier to carry the RF signal and the AC power down individual streets. The distribution line can be tapped into and used to connect the individual drops to customer homes and businesses.
By using frequency division multiplexing, an HFC network can carry a variety of services, including: analog TV, digital TV (SDTV or HDTV), video on demand, telephony, and high-speed data.
The HFC network can be operated bi-directionally, so that signals are carried in both directions on the same network from the headend/or hub office to the home or business, and from the home or business to the headend or hub office. The forward-path or downstream signals carry information from the headend or hub office to the home, such as video streaming, voice and internet data. The return-path or upstream signals carry information from the home or business to the headend or hub office, such as control signals to order a movie or internet data or to send an email. The forward-path and the return-path are often carried over the same coaxial cable in both directions between the optical node and the home or business.
An optical fiber can comprise: a core, cladding, and a buffer providing a protective outer coating, in which the cladding guides the light along the core. The core and the cladding, which has a lower-refractive-index, can be made of high-quality silica glass, although they can both be made of plastic as well. Connecting two optical fibers can be accomplished by fusion or mechanical splicing. Two main types of optical fiber used in optic communications include multi-mode optical fibers and single-mode optical fibers. A multi-mode optical fiber has a larger core (≧50 micrometers), allowing less precise, inexpensive transmitters and receivers to connect to it and cheaper connectors. A multi-mode fiber, however, can cause multimode distortion, which often limits the bandwidth and length of the link. Multi-mode fibers are often expensive and exhibit higher attenuation. The core of a single-mode fiber is smaller (<10 micrometers) and requires more expensive components and interconnection methods, but allows much longer, higher-performance links. In order to package fiber into a commercially-viable product, it is typically protectively-coated by using ultraviolet (UV), light-cured coating such as acrylate polymers, then terminated with optical fiber connectors, and finally assembled into a cable.
The choice between optical fiber and electrical (or copper) transmission for a particular system is made based on a number of trade-offs. Optical fiber is generally chosen for systems requiring higher bandwidth or spanning longer distances than electrical cabling can accommodate. The main benefits of fiber are its exceptionally low loss of signals allowing long distances between amplifiers/repeaters, its absence of ground currents, other parasite signal and power issues common to long parallel electric conductor runs, and its inherently high data-carrying capacity. Thousands of electrical links would be required to replace a single high bandwidth fiber cable. Another benefit of fibers is that even when run alongside each other for long distances, fiber cables experience effectively no crosstalk, in contrast to some types of electrical transmission lines. Fiber can be installed in areas with high electromagnetic interference, such as alongside utility lines and power lines. Optical fibers are now also increasingly used to carry signals over very short distances within individual electronic devices because of their extremely large bandwidth and ability to carry large amounts of data over a single fiber in both directions simultaneously.
The transmission distance of a fiber-optic communication system has traditionally been limited by fiber attenuation and fiber distortion. By using optical-electronic repeaters, these problems have been minimized or eliminated. Optical electrical repeaters convert the signal into an electrical signal, and then use a transmitter to send the signal again at a higher intensity than it was before. An alternative approach is to use an optical amplifier, which amplifies the optical signal directly without having to convert the signal into an electrical signal. It can be accomplished by doping a length of fiber, such as with the rare-earth mineral erbium, and pumping it with light from a laser with a shorter wavelength than the communications signal. Optical amplifiers have largely replaced optical-electrical repeaters in new installations.
Optical fibers can break if bent to a very small radius. If an optical fiber is bent too sharply, signals from light traveling in the core of the fiber can actually escape through the cladding and be lost.
Many electronic devices, including portable ones, for which minimizing their size is a significant design goal, employ mechanisms, such as hinges, for folding parts of the device upon each other to expand or contract the access or profile of the device as needed. Generally, at least some circuits within a base part of the device on one side of a hinged connection have to electronically communicate with circuits in another part of the of the device and must cross the hinges. Such requirements present design difficulties in terms of creating a flexible and/or moveable on electrical signal path that can survive repeated bending, flexing, translation or other movement.
Presently, there is no solution in the market place to protect optical fibers as they cross the hinge-line of a HFC optical node. For optical nodes used in line pole pedestal applications, the management of fibers is crucial. There are two sides to these optical nodes; one is considered the base and the other is considered the lid. In general, the fiber optical cable from the plant enters the lid side of the product. Once inside the product, the fiber is managed via fiber trays instituted inside the node. The fiber then terminates into the optical transmitters and receivers that are also in the lid side of the node. The problem is that when these optical modules are installed in the base side of the node, then the fiber needs to cross what is called the hinge-line of the node. This is the area where the node opens and closes and in this area the fiber has high risk of getting pinched.
Some conventional nodes and hubs, separate RF and optical portions with a conventional arrangement in which only electrical connections cross the lid hinge. This arrangement still has the potential for pinched wires and stress on termination connectors. In other conventional nodes and hubs, the customer must resort to self-help to coil and secure the numerous fiber jumpers crossing the hinge. In still other conventional nodes and hubs, different types of plastic spiral wrap and holders are used to secure cables crossing the hinge, but these more rigid solutions have been a major source of customer complaints due to connector stress and intermittent connections.
A living hinge is a thin flexible hinge. It is typically thinned or cut to allow the rigid pieces to bend along the line of the hinge. The minimal friction and very little wear in a living hinge makes it useful in the design of microelectromechanical systems. Living hinges can flex more than a million cycles without failure. Historically, in 1957, an unusual phenomenon was noticed by engineers studying pigment dispersion in very thin-walled color chips. Below a certain thickness, polypropylene molecules oriented in the direction of flow. Bending perpendicular to this orientation resulted in a stronger part that did not break with repeated flexing. Bob Munns, coined the term “living hinge” and the name stuck. The living hinge has been since used in numerous products.
It is, therefore, desirable to provide an improved bridge for use with optical fibers, such as for use in a broadband network.